DAMAGE TO URACIL- AND ADENINE-CONTAINING BASES, NUCLEOSIDES, NUCLEOTIDES AND POLYNUCLEOTIDES: QUANTUM YIELDS ON IRRADIATION AT 193 AND 254 NM

Abstract Photoreactions, such as base release and decomposition of the base moiety, induced by either 20 ns laser pulses at 193 nm or continuous 254 nm irradiation, were studied for a series of uracil and adenine derivatives in neutral aqueous solution. The quantum yield of chromophore loss (φ) depends significantly on the nature of the nucleic acid constituent and the saturating gas (Ar, N₂O or O₂). In the case of polynucleotides the destruction of nucleotides was measured by high-performance liquid chromatography after hydrolysis; the quantum yields (φ) are comparable to those of chromophore loss or larger. The φ_cl and aφ_dn of 0.04–0.1 for poly(U) and poly(dU), obtained for both wavelengths of irradiation, are due to processes originating from the lowest excited singlet state, i.e. formation of photohydrates and photodimers, and a second part from photoionization using λ_irr= 193 nm. Irradiation at 193 nm effectively splits pyrimidine dimers and thus reverts them into monomers. The quantum yield for release of undamaged bases (φ_br) from nucleosides, nucleotides and polynucleotides upon irradiation at 254 nm is typically φ_br= (0.1–1) × 10^?4 Breakage of the N-glycosidic bond is significantly more efficient for λ_irr=193 nm, e.g. φ_br= 1.1 × 10^?3, 0.8 × 10^?3, 4.3 × 10^?3 and 0.5 × 10^?3 for poly(A), poly(dA), poly(U) and poly(dU) in Ar-saturated solution, respectively. Enhanced φ values for λ_irr= 193 nm, essentially for adenine and its derivatives, are caused by photo-processes that are initiated by photoionization.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

PHOTOLESIONS IN DNA UPON 193 nm EXCITATION

Aqueous solutions of plasmid (pBR322 and pTZ18R) and calf thymus DNA were excited by 20 ns laser pulses at 193 nm. The quantum yields of single- and double-strand break formation, interstrand cross-links, locally denatured sites, (6–4)photoproducts and biological inactivation (Φ_ssb, Φ_dsb, Φ_icl, Φ_ids, Φ_6–4 and Φ_ina, respectively) were measured. The quantum yields are virtually independent of intensity, demonstrating a one-quantum process. The obtained values in aerated neutral solution in the absence of additives are Φ_ssb= 1.5 × 10^--³, Φ_dsb, = 0.06 × 10^--³ (dose: 10–200 J m^-2), Φ_icl=Φ_Ids= 0.1 × 10³ and Φ_6–4= 0.5 × 10^--³ Both Φ_ssb and Φ_dsb decrease strongly with increasing concentrations of TE buffer (0.01–10 m M ). Biological inactivation of the pTZ18R plasmid was determined from the transformation efficiency of Escherichia coli bacteria strains AB1157, AB1886 uvr and A82480 uvr rec; the Φ_ina values are 1.4 × 10³, 2.1 × 10³ and 3 × 10^--³, respectively. The monoexponential survival curves in all cases show that a single damage site leads to inactivation (one single hit). The biological consequences of different photoproducts are discussed.     

PHOTOLESIONS AND BIOLOGICAL INACTIVATION OF PLASMID DNA ON 254 nm IRRADIATION AND COMPARISON WITH 193 nm LASER IRRADIATION

Plasmid pTZ18R and calf thymus DNA in aerated neutral aqueous solution were irradiated by continuous 254 nm light. The quantum yields are φ_ssb= 4.0 × 10^-5 and φ_dsb= 1.4 × 10^-6 for single- and double-strand break formation, respectively, φ_br= 2.3 × 10^-5 for base release, φ_dn= 2.1 × 10^-3 for destruction of nucleotides, and φ_icl×φ_lds× 1 × 10^-6 for interstrand cross-links and locally denatured sites, respectively. The presence of Tris-HCI/ ethylenediaminetetraacetic acid (10:1, pH 7.5) buffer strongly reduces φ_ssb, The corresponding φ values, obtained on employing pulsed 193 nm laser irradiation, are much larger than those using λ_irr, = 254 nm. This is ascribed to a contribution of chemical reactions induced by photoionization, which is absent for 254 nm irradiation. The quantum yields of inactivation of plasmid DNA (λ_irr= 254 nm) were measured by transformation of the Escherichia coli strains AB1157 (wild type), φ_ina(1157) = 1.6 × 10^-4, AB1886 (uvr^-), φ_ina(1886) = 4.2 × 10^-4, AB2463 (rec^-), φ_ina(2463) = 4.1 × 10^-4 and AB2480 (uvr^- rec^-), φ_ina(2480) = 3.1 × 10^-3. The quantum yields of inactivation of plasmid DNA are compared with those of the four E. coli strains (denoted as chromosomal DNA inactivation) obtained from the literature. The results for E. coli strain AB2480 show that the chromosomal DNA and the plasmid DNA are both inactivated by a single pyrimidine photodimer per genome. With the E. coli strain AB2463 inactivation of plasmid and chromosomal DNA is the same for the same total damage per genome and is ～ 10 times smaller than for AB2480. This is explained by photodimer repair in chromosomal and plasmid DNA and by the absence of dsb repair in both cases. In the repair wild-type strain AB1157, inactivation of the plasmid DNA is roughly 100 times higher than that of the chromosomal DNA. We postulate that a portion of this difference is due to repair of dsb by the recA system in chromosomal DNA and that such repair does not take place in the plasmid DNA. The biological results from 254 nm irradiation are compared with those from 193 nm laser irradiation.     

MECHANISM OF HIGH POWER PICOSECOND LASER UV INACTIVATION OF VIRUSES AND BACTERIAL PLASMIDS

Abstract— The mechanism of inactivating action of high-power picosecond laser UV radiation (λ= 266 nm) on the λ and φX174 bacteriophages and the pBR 322 plasmid has been studied. It has been shown that at UV radiation intensities from 10¹¹ to 10¹³ W/m², inactivation of viruses and bacterial plasmids occurs mainly on account of single-strand breaks in the DNA chain unlike the case of less powerful UV radiation where the inactivation is associated with the formation of pyrimidine dimers.     

Silver nanocube-enhanced far-red/near-infrared fluorescence of conjugated polyelectrolyte for cellular imaging

We present the study of silver nanocube (Ag NC)-enhanced fluorescence of a cationic conjugated polyelectrolyte (CPE) for far-red/near-infrared fluorescence cell imaging. Layer-by-layer self-assembly of polyelectrolytes on 78 nm Ag NCs is used to control CPE-metal distance and its effect on CPE fluorescence. The highest fluorescence enhancement factor (FEF) is obtained for Ag NCs with two bilayers, corresponding to a CPE-metal spacer thickness of ～6 nm. At the optimal excitation wavelength, the FEF is 13.8 with respect to the control silica nanoparticles (NPs). The fluorescent NPs are further used for cellular imaging studies. The CPE-loaded Ag NCs with two bilayers exhibit excellent image contrast, superior to the control of CPE-silica NP at a similar uptake efficiency. The viability test indicates low cytotoxicity of the CPE-loaded Ag NCs, rendering them as promising cell imaging agents.     

Observation of low‐wavenumber out‐of‐plane optical phonon in few‐layer graphene

Few‐layer graphene grown by chemical vapor deposition has been studied by Raman and ultrafast laser spectroscopy. A low‐wavenumber Raman peak of ~120 cm⁻¹ and a phonon‐induced oscillation in the kinetic curve of electron–phonon relaxation process have been observed, respectively. The Raman peak is assigned to the low‐wavenumber out‐of‐plane optical mode in the few‐layer graphene. The phonon band shows an asymmetric shape, a consequence of so‐called Breit‐Wigner‐Fano resonance, resulting from the coupling between the low‐wavenumber phonon and electron transitions. The obtained oscillation wavenumber from the kinetic curve is consistent with the detected low‐wavenumber phonon by Raman scattering. The origin of this oscillation is attributed to the generation of coherent phonons and their interactions with photoinduced electrons. Copyright © 2012 John Wiley & Sons, Ltd.     

Reply to “A comment on “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth gravity model,by I. Ciufolini et al.””

In 2016, we published “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth’s gravity model. Measurement of Earth’s dragging of inertial frames [1]”, a measurement of frame-dragging, a fundamental prediction of Einstein’s theory of General Relativity, using the laser-ranged satellites LARES, LAGEOS and LAGEOS 2. The formal error, or precision, of our test was about 0.2% of frame-dragging, whereas the systematic error was estimated to be about 5%. In the 2017 paper “A comment on “A test of general relativity using the LARES and LAGEOS satellites and a GRACE Earth’s gravity model by I. Ciufolini et al.”” by L. Iorio [2] (called I2017 in the following), it was incorrectly claimed that, when comparing different Earth’s gravity field models, the systematic error in our test due to the Earth’s even zonal harmonics of degree 6, 8, 10 could be as large as 15%, 6% and 36%, respectively. Furthermore, I2017 contains other, also incorrect, claims about the number of necessary significant decimal digits of the coefficients used in our test (claimed to be nine), in order to eliminate the largest uncertainties in the even zonals of degree 2 and 4, and about the non-repeatability of our test. Here we analyze and rebut those claims in I2017.     

Ferrocenyl-functionalised terpyridines and their transition-metal complexes: syntheses,structures and spectroscopic and electrochemical properties

Terpyridine ligands of the type Fc'-X-tpy (Fc'=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy'=4'-substituted 2,2':6',2'-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor-sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc' groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc' and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.     

Solvent-dependent C-OH homolysis and heterolysis in electronically excited 9-fluorenol: the life and solvation time of the 9-fluorenyl cation in water

The primary pathways of the photodecomposition of 9-fluorenol (FOH) were studied in polar and nonpolar solvents by use of laser flash-photolysis with a resolution time of 10 ps. In solvents of high polarity, that is, in 1,1.1,3,3,3-hexafluoroisopropanol (HFIP), 2,2,2-trifluoroethanol (TFE), formamide or water, the fluorenyl cation, F+, forms by heterolytic C-O bond cleavage. In H2O, the initial (10 ps) spectrum of F+ has lambdamax at <460 nm. This absorption red-shifts with T = 25 ps to the "classical" spectrum with lambdamax = 510-515 nm. This process is assigned to the solvation of the initial "naked" cation, or rather, the contact ion pair. The lifetime of the solvated fluorenyl cation in H2O (or D2O) and TFE was measured to be tau 20 ps and 1 ns, respectively. In solvents of lower polarity such as alkanes, ethers and alcohols, the long-lived (tau 1/2 1 micros) fluorenyl radical, F., (lambdamax = 500 nm) forms through homolytic C-O cleavage. In addition to the radical and the cation, the vibrationally relaxed excited singlet state of FOH is seen with its absorption at approximately 640 nm; its lifetime is strongly dependent on the solvent, from 10 ps for formamide to 1.7 ns for cyclohexane. The rate constant for singlet decay increases exponentially with the polarity of the solvent (as expressed by the Dimroth-Reichardt ET value) or with the Gutmann solvent acceptor number. The relaxation of S1 to S0 is accompanied by homolytic C9-O bond cleavage (except in HFIP, TFE, and water, where S1 is not seen).